Funnelling effect magnified impact of typhoon Haiyan

Devastation wrought by typhoon Haiyan in the Philippine city of Tacloban was probably intensified by a landscape that funnelled a 5-metre-high storm surge over the city. Higher sea levels due to global warming may have also worsened the effects.

That's the message from storm specialists contacted by New Scientist. "Tacloban is tucked into what is essentially a bay, so the storm surge got driven straight into it," says Julian Heming, the tropical prediction specialist at the UK Met Office.

The hurricane itself is thought to be the most powerful on record to make landfall, with wind speeds sustained over a minute hitting 314 kilometres per hour (195 miles per hour). "The nearest to this is Hurricane Camille in 1969, which reached 190 mph at landfall," says Heming.

Interplay of factors

What made the damage and death toll so high was the unfortunate interplay between the power and direction of the typhoon and the landscape around Tacloban.

The storm was funnelled through the channel separating the island of Samar to the north-east from the province of Leyte to the south-east. Tacloban sits on a promontory poking into the channel, and so was completely exposed as the surge approached and gained height in the shallower waters closer to land.

Rising seas

Another contributing factor could be rises in sea level this century around the Philippines. Global satellite data between 1992 and 2013 show that the Philippines is a hotspot for sea level rise. Climate scientists have been warning for some years that rising sea levels would pile more water into storm surges and worsen their impacts.

There's also data going back to 1947 from tide gauges in Albay, a province on Luzon Island, to the north-west of Samar, showing that the sea level has risen 30 centimetres in the Philippines over the past 60 years. "These rises seem particularly high," says Aslak Grinsted of the University of Copenhagen in Denmark. Grinsted says that higher sea levels may have worsened the impact of Haiyan.

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Typhoon Haiyan battered the Philippine city of Tacloban (Image: Erik de Castro/Reuters)